Merge branch '5.1'

* 5.1:
  Tweak
  Update validation.rst
  update building locally without docker docs
  Update chatters.rst

Author: javiereguiluz

contributing/documentation/overview.rst

@@ -273,7 +273,8 @@ If you don't use Docker, follow these steps to build the docs locally:
 
    .. code-block:: terminal
 
-        $ pip install sphinx~=1.3.0 git+https://github.com/fabpot/sphinx-php.git
+        $ cd _build/
+        $ pip install -r .requirements.txt
 
 #. Run the following command to build the documentation in HTML format:
 

notifier/chatters.rst

@@ -77,7 +77,7 @@ some interactive options called `Block elements`_::
             ->text('The Symfony Community')
             ->accessory(
                 new SlackImageBlockElement(
-                    'https://example.com/symfony-logo.png',
+                    'https://symfony.com/favicons/apple-touch-icon.png',
                     'Symfony'
                 )
             )

validation.rst

@@ -119,8 +119,8 @@ following:
 .. index::
    single: Validation; Using the validator
 
-Using the ``validator`` Service
-~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+Using the Validator Service
+~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
 Next, to actually validate an ``Author`` object, use the ``validate()`` method
 on the ``validator`` service (which implements :class:`Symfony\\Component\\Validator\\Validator\\ValidatorInterface`).